Study On Yb Doped Mixed Fluoride Laser Crystals

Since the first diode laser pumped Yb doped yttrium aluminum garnet （Yb:YAG） laseroperation reported at room temperature in1991, Yb3+ion doped the laser crystal has been attractedextensive attention and rapid development in recent years, with the development of high energylaser semiconductor technology. Yb ion possess the simplest energy level structure with anelectronic configuration of4f¹³, consisting of only two levels: the2F7/2ground state and the2F5/2exited state. Due to its very simple energy level scheme, Yb ion has several advantages: no excitedstate absorption, no up-conversion, and no concentration quenching. The crystal of Yb-dopedfluoride has broadband absorption and emission spectra, a relatively long fluorescence lifetime, andhigh fluorescence quantum efficiencies, which has been recognized to be favorable hosts for lasingon high power, wavelength tunable and/or femtosecond laser operation. This study focused on thecrystal growth, structure, spectra and laser properties of CaF₂-SrF₂and CaF₂-YF₃mixed fluoridecrystals, obtained by vertical Bridgeman or TGT method. Main contents are as follows:The crystal lattice constant, Yb³⁺segregation coefficient, thermal conductivity, absorptionspectra, emission spectra and fluorescence lifetime in Yb:（1-x）CaF₂-xSrF₂changed with thevariation of CaF₂/SrF₂ratio. It can be seen from the optical properties that different opticalproperties with different components of Ca/Sr proportion. When the Ca/Sr ratio is close to1:1, theYb³⁺ion has larger absorption and emission cross section than Yb-doped CaF₂crystal.For the low-temperature spectra, Yb: Ca_0.5Sr_0.5F₂crystal has larger absorption cross sectionand wider luminesce spectra than Yb:CaF₂at long-wave lengths, Yb³⁺ion level splitting levelsplitting was calculated according to the spectroscopic properties of Yb: Ca_0.5Sr_0.5F₂crystals at lowtemperatures. The Yb³⁺ion level splitting is larger in Ca_0.5Sr_0.5F₂crystal than CaF₂crystal. Thelaser performance parameters of Yb: Ca_0.5Sr_0.5F₂crystal were calculated theoretically. Lowthreshold, high efficiency laser crystal in the Yb³⁺doped Ca_0.5Sr_0.5F₂crystal is greatly anticipated.The near infrared spectra of Yb ion doped CaF₂-YF₃system are different according to thedifferent components. When Y:Yb ratio increases from1:1to2:1, the luminescence intensity andfluorescence lifetime increases. The results are similar with Yb, Na doped CaF₂for opticalproperties and fluorescence lifetime, but the absorption and emission cross section are higher thanYb, Na doped CaF₂crystal. This shows that codoping Y not only suppress the formation of Yb³⁺-Yb³⁺cluster but also change the local crystal lattices of Yb ions.